The aim of this research project is the elucidation of the biochemical mechanisms of interferon action. Our work has emphasized the study of the following enzymatic activities believed to be involved in interferon action: 1) the 2',5'An synthetase, 2) the protein kinase which phosphorylates the 67K protein, 3) the 2',5'An phosphodiesterase, and 4) the 2',5'A -dependent RNase, RNase F. These studies have been divided into two approaches: 1) the role of polynucleotide structure to the activation of the 67K protein kinase activity and protein synthesis inhibition and 2) the role of the above mentioned enzymatic activities in the establishment and maintenance of the anti-viral effects of interferon.